Process of coating with thermoplastic material



B. c. MlLLER March 4,` 1947.

PRO-C1555 0F COATING WITH THERMOPLASTIC MATERIAL AFiled sept. 19, 1939 NVENTOR BERT C MILLER -Brsr AVAILABLE comr Patented Maro 4, 1947 i 2,417,909 ,Np-"tr QFFICEFA PLASTIC MATERIAL Bert C. Miller, Montclair, N. J.; assigner to Bert C. Miller, Inc., East Orange,fN. Jara( corporation of New York Application spt'einber 19,1939;seriaiN0.295,571

y 1 Claim. n (ci. 117-64) This invention relates to'a method for `the molten application of thern'lopl 'asticy coating materials to suitable bases for providingfcoatings thereon.

It has been proposed to apply coating'materials in a molten condition to various' bases such as paper, cloth, structureless foil and -they like as for example, by dipping a Sheet orpassing a web through a molten bath; dipping'asmooth roll into a molten .bath and transferring the lm.

from the surface of the roll to a base sheet but such processes have been subject to one or more difficulties. Where the sheetl or 'web is dipped into or passed through a bath of molten'material there is usually a great deal of impregnation of the base and it is difficult, if notimpossible, t

e obtain a smooth uniform coating by any subsequent treatment.- Where a roll dipsinto a bath of molten coatingmaterial diiculty is experienced in providing a film of `uniform thickness and it has been proposed to control the thickness of the lm vby using n ip rolls instead of stationary doctoring means, and by this method more accurate control has been attained. Any roll method of application heretofore known has'not produced a uniform or continuous lcoating on the surface of the base and a subsequent step of smoothing was required.

This invention seeks to provide a method and apparatus for the application of molten thermoplastic materials to provide either a coating as t 2 Y Y. l plied to the base.l e With constructions of the type just described,`the molten material may be appliedto the' surface of the roll and this material will fill the recesses or depressed portions and also, to a more or less extent, coat the elevated,

or what has been described as the normal, sur-` face of the roll. rTo secure a control of the amount of material to be applied `as -determined 'f by the extent of the recesses, the molten material `on the normal surface of roll is doctored and thereby removed conveniently by areslient blade which scrapesthe entire width of the roll; The

' doctormay be stationary but preferably oscilhereinafter defined on a base, sheet or a particular form of coating in the form of a substantially continuous film without encountering the diillculties of the priorl art procedures as generally set forth above.

l't has been found that an accurate control of the amount of coating material applied to the base can be secured by employing a heated roll provided with a surface which is not smooth but lates parallel to the axis ofthe roll.

Alternatively, it is vpossible to control the amount of material to be applied by using a relatively smooth roll and doctoring the surface of that smooth roll to form a coating on the surface of the smooth roll which is discontinuous.

This may be accomplished by the use of a' pair of doctor blades in contact with eachother'and generally resembling combs which are reversely oscillated. With this arrangement, a substantially continuous filmv on the surface of the roll passes under the doctor blades having `teeth which are in direct contact with the roll and, therefore, remove at leastl some of the coating from the surface. As the doctor blades reciprocate, the

openings between the teeth will coincide and the coating material on the surface ofthe roll will pass between the teeth but the continued reciprocation of the doctor blades will soon close the opening and cut off the film. The molten coating material on the heated roll behind the doctor blades is in the form of a large number of individual small mounds-substantially the reverse of those on the etched roll. With anothervform of reciprocation between the doctor blades, the

- coating material on the surface of the roll behind which has elevational differences such as a no rmal surface and depressed portionsfrom the nor.- mal surface according-to a pattern. The depressed portions may conveniently be made by etchingthe surface of the roll to form a large number of minute independent pockets the size and shape of which will vary according` to the` amountof material, it is desiredto apply to the base.` While it is suggested to etch the roll, other means such' as mechanical engraving might be employed,` for providing the independent pockets` or providingrecesses Vas hereinafter described.`

It is also proposedjaccording to this `invention to provide recesses from the normall surface` of the rollwhich might beV describedl as ofthe nature of `knurlingwhich `comprises aipluralityv of diagonal inte'rse'ctinggrooves` adapted'to receive the moltenfcoating material and in Whichtth/e.

width, depth and spacingfof the grooves :determines the'amount of material that will be apthe blades might be in the form of intersecting continuouslines resembling knurling. By properlyadjufsting the rate of travel of the surface of the roll, the size and shape of the teeth of the ,doctor blades and the rate and relative scillation of these blades, the molten material on the surface of the heated smooth roll will form a discontinuous coating according 'to a pattern and may generally resemble intersecting ribs or may be individual minute discrete droplets, a single oscillating or,l non-oscillating comb doctor would give parallel `ribs of coating.' All such forms hereinbefore described as taken by the material in its application to. a web are generically referred to as mounds e When a sheet of base materiaLusually inthe form of a web, is brought into contact with the roll, the molten coating material in thetrecesses onthe surface of theroll or patterned above the surface 4of a smooth roll. is transferred from the roll to the'base and generally follows the exactv be applied but merely suggestive.

has. when proceeding as above described, a Sen...

erally uniform although not continuous coating.

- Such a sheet may for some purposes, as in the decorative field, be of utility. The coating does not usually have any particular gloss because of the non-uniformity of reflection and refraction of light from the irregular coating. Some improvement is secured by a rapid hot blast which may smooth the surfaces of individual dots or ribs. In order to provide a uniform glossy'surface, the coating on the sheet is'fused by bringing it into contact with a heated smoothing element which, by melting and mechanical action, blends the discrete particles or the patterned portions' of the coating into a substantially continuous film of high gloss and having characteristics of moisture-proofness and the like consistent with the properties of the coating material.

It will be understood that by controlling lthe relative size and depth of the recesses or the action of the doctor blades on the smoother roll the weight of the coating applied to the base can be very accurately controlled and the application is very uniform. For example, if a roll is prepared to apply five pounds of coating material per ream this exact amount will always be applied. Similarly, if the roll is so constructed as to apply ten pounds per ream the coating will be uniformly of that weight. The iigures above given are not the limits of the amounts which may It has been found that coatings of even less weight than live pounds and substantially greater then ten poundsv can readily be applied and may be used depending upon the properties desired in the final product.

The coating materials must be ofthe type identified as thermoplastic and are usually materials which are solid at normal temperatures, except where the coating is used as a laminating adhesive, and preferably has a relatively sharp melting point to produce a complete melt at temperatures not substantially exceedingv about 300 F. although materials having higher melting points may under some circumstances` and with certain bases be successfully employed. The process and apparatus as herein described is particularly useful for the molten application of essentially resinous materials and may comprise either natural or synthetic resins having the physical properties above described. Other factors influencing the selection of the resins used in the molten coating compositions will be evident to those skilled in the art.

. The coating composition for application in molten form is melted before application to the surface of the roll. In some cases it may be desirable to mix the various ingredients inl a separate vessel to which heat can be applied or solid materials may, in some instances, be added directly to the molten bath in the apparatus, although it is usually preferable to add the coating material in a molten form to the bath. Means should also b e provided for maintaining the bath in a molten condition.

Similarly, the coating roll whether engraved,

etched or smooth must be maintained at a temperature suiiicient to keep the coating material on its surface in a vmolten vcondition until it is transferred to the web. A metal roll is used preferably cast iron or steel with a copper electrov plate surface for etching or engraving and a `nnal chromium plating. Internal heating means will serve although it is extremely difficult to uniformly heat the roll by internal heating. In one of the preferred forms of this invention internal heating of the roll'by extraneous heat sources such as hot oil, electric resistance elements and the like is dispensed with and the roll is heated solely by the bath of molten material. Uneven heating warps the roll making uniform application impossible. .To heat the roll by the bath of molten material which provides uniform heating, the apparatus must include means for applying substantial heat to the bath and for keeping the material in motion although the latter is usually accomplished by rotation of the4 lroll. The roll, inorder to make up for the heat losses to be web` being coated, must be substantially submerged in the molten bath. By substantially submerged it is intendedthat at least one-half and preferably three-quarters of the roll -be submerged when the bath is unagitated. Rotation of the roll will somewhatl effect the extent of submersion. With this arrangement in the molten bath, it-has been found that the roll is kept at a proper temperature to carry the film of molten coating material and transfer it l to the sheet or web.

In the attached drawings there is illustrated anapparatus constructed in accord with certain of the teachings of this invention which is i1- lustrative of the principles of the invention applied to a preferred embodiment. f

Figure 1 is a view in side elevation with a part broken away in section showing the coating apparatus; and

Figure 2 is a top plan view of the apparatus shown in Figure 1 with a portion of a roll broken away to show the coating roller.

Referring now to the drawings, reference numeral |02 is a tank for containing the molten coating material |04 which may be supplied through an opening (not shown) either in the side or the top of the tank |02. The tank 02 is jacketed as at |06 to form a compartment substantially surrounding the tank and adapted to receive a heating fluid, as for example, oil, supplied and withdrawn through the conduits ||0 and H2. Legs |05 support the apparatus. Mounted within the tank |02 is a roll I4 mounted on a shaft I6 journalled in the sides of the tank and one end of which projects through one side of the tank to receive a keyed pulley H8 driven by a belt |20. AThe shaft ||6 is so positioned within the tank |02 that only a small portion of the entire roll ||4 extends out of the e0 top of the tank making it possible to submerge substantially the entire roll where necessary. As 'illustrated in Figure 1 the upper level |22 of the coating material |04 is above the axis of the roll -||4. The top of the tank |02 is substantially 05 closed by a cover plate |24 that also serves as a base on which to mount certain rolh or other apparatus hereinafter described, there being only sumcient opening |26 in the cover |24 to permit the exposure of a small section at the extreme top of the roll ||4.

The roll |l4 is rotated in a clockwise direction when viewed as in Figure 1 and a section of the surface of the roll ||4 after leaving the bathl |04 passes under a doctor blade |28 preferably constructed of spring steel and which may have additional support for mounting on a shaft |32 journalled in bearing brackets |34, |34' for oscillatory` reciprocation. The shaft |32 extending through the bearing bracket |34' is provided at its end with a grooved collar |36 or other means to retain a spring |38 between the bearing bracket.

|30 and the end of the shaft |32 and also for connection to a pivoted lever |40 as by the pin |42. Serving as the pivot for the pivoted lever |40 is Ia bracket |44 mounted on the side of the jacket |06. The other end of the pivoted lever |40 projects toward the shaft I|6 on which is mounted a cam wheel |46 for engagement with a roller |48 on the end of the pivoted lever |40. Rotation of with a roller having elevational differences on its surface as above described. The roll I|4, rotating in clockwise direction as it leaves the bath |04, has a surface coating which is carried to the doctor blade |28 where all of the coating material on the normal surface is removed leaving only that which is in the depressions. It will be evident that where the roll |I4 is provided with a smooth surface, a double toothed doctor blade may be substituted. for the single blade 28 as above described. As shown in Figure 2 the roll ||4 has depressions in its entire circumferential surface except at the ends ||5 which may be smoothed and at the normal surface of the roll. The sheet or web may or may not extend over the end surface ||5 but in those cases where it does, no coating will be applied. The roll may be designed for spot applicaion.

Behind the doctor blade and substantially at the top ofthe roll I I4 is a pressure roll |50 mounta wind-up roll.

ing Ibar |64 and the adjustable roll |14 it is possible to control the extent of the curved surface |66 in contact with the web and the angle at which the web leaves over the sharp edge of the curved surface |66 in accord with operating requirements for adequate smoothing,

In operation the belt |20, driven by any suitable source of power, drives the pulley I8 fixed to the shaft IIB, thereby rotating the coating roll ||4 and the cam wheel |46. A web |62 guided by the roll |60 is threaded between pressure roll |50 and coating roll I I4, over the smoothing bar |66 under the control of adjustable roll |14 and to As the web passes between pressure roll |50 and the coating roll II4 it picks up the coating material on the roll H4 either from the depressions if that type of roll is used or from the surface where the coating material has been applied to the smooth surface to give a ed on a shaft |52 journalled in bearing brackets v |54 and provided with an eccentric handle |56 to adjust the relative position of the pressure roll |50 and the coating roll ||4. The pressure roll |50 is preferably relatively small to create a short nip and made of a resilient material atleast at i its surface to provide resilient uniform pressure across the entire roll |I4 as the web passes between these two rolls.

Also mounted on the cover |24, in brackets |56,

may be a guide roll to guide-a web |62 from a supply roll'(not shown) to between the presv s ure roll |50 and the coating vroll |I4.

The web, after passing between'the said rolls, ls drawn over a smoothing bar |64 which at its outer edge is provided with a smooth curved surface ending in a relatively sharp edge at the point where the web |62 leaves the smooth curved surface. The smoothing bar |64 is adjustable for pivoting about its axis 66 under thev control smoothing bar |64 must be uniformly heated by means not shown in Figures 1 and 2 whereby the discontinuous coating applied to the lower surface of the web |62 is smoothed in passing over the curved surface I 66 to form a continuous film. Associated with the smoothing bar |64 and also mounted as by brackets |12 onv the cover |24 is an` adjustable roll |14. The adjustable roll |14 may be on pivot arms |16 the positions of which are controlled by the lever |18. With the adjustable cooperative relation between the smooth.

,of a lever |10. The curved surface |66 of the generally uniform but discontinuous coating.v

After cooling (there being no solvent to evaporate) the web can be rewound but where a continuous ilm is desired, especially one with a high gloss the web passes from the coating roll over the heated smoothing bar |64 where the discontinuous coating is smoothed to form a substantially continuous film. After the coated sheet is cooled it is rewound.

While the -invention has been particularly described with'reference to the illustrated embodiment, this is to be considered simply as illustrative of the invention because all of the steps or parts shown need not be used in the specific combinations and various substitutes may be used in the combination without departing from the spirit and scope of the invention as will be evident to those skilled in the art.

What is claimed is:

The method .of coating sheet material with high melting thermoplastic material having a sharp melting point not substantially exceeding about 300 Fi, comprising printing a surface of a continuously advancing web of sheet material with said thermoplastic, heated to a liquid state, to form relatively closely spaced but segregated and uniform quantities, and thereafter spreading and smoothing the thus-applied thermoplastic material, in a. single step, into a continuous even lm solely by the conjoint simultaneous application of heat and lspreading pressure to the printed surface of the said continuously advancing web. BERT C. MILLER.

REFERENCES CITED UNITED STATES PATENTS Number Name Date 2,170,140 Grupe Aug. 22, 1939 "2,100,712 Emmey Nov. 30, 1937 2,157,286 Emmey May 9, 1939 1,911,592 Supligeau May 30, 1933 1,791,040 Richardson Feb. 3, 1-931 2,033,379 Jenkins Mar. 10, 1936 '856,886 Kubler June 11, 1907 2,117,200 Miller May 10, 1938 2,142,666 Bucy Jan. 3, 1939 2,185,859 Massey Jan. 3, 1940 2,199,228 Obenshain et al Apr. 30, 1940 2,163,712 Shearer June 27, 1939 FOREIGN PATENTS Number Country Date 428,559 British May 15, 1935 British ....-..s Dec. 3. 1934 

